Keep VLF Count in check for all your transaction log files. Too many VLFs can cause slow DB Recovery & performance Hit.
Use Set NOCOUNT ON for all Batches, Stored Procedures and Triggers to reduce Network traffic for SQL Server.
Grant Granular access whenever possible to avoid providing elevated access.
The KEEP PLAN query hint changes the recompilation thresholds for temporary tables, and makes them identical to those for permanent tables. Therefore, if changes to temporary tables are causing many recompilations, this query hint can be used.
Disable xp_cmdshell unless it is absolutely required.